HLRB-II: Recommendations on tuning of large scale I/O
publish at lrz.de
Fr Mär 4 15:33:56 CET 2011
Recently, we have seen intermittent degradation of I/O performance on
the HLRB-II. The exact root cause of this degradation is being
investigated. However, there are measures that you as the users of the
system can take to optimize your own program's I/O performance.
For tuning of I/O, SGI provides a special shared library called FFIO
(Fast and Flexible I/O), the use of which is recommended. In
particular, FFIO allows to perform unbuffered I/O, which for large
files should give much better performance. The FFIO facility requires
the following information, which is stored inside environment
1. A pattern for the file names for which FFIO should be used
2. Some parameters for tuning (note that FFIO will need additional
For running MPI programs together with FFIO a special run script
mpiexec_ffio must be used.
A more detailed description on how to use FFIO is available at http://
www.lrz.de/services/compute/hlrb/files/ under the heading Efficient use
of IO -> FFIO layer.
If you encounter any difficulties with using FFIO, or if you see that I
/O performance does not improve even with FFIO switched on, please
contact the LRZ service desk and provide a detailed description of your
This information is also available on our web server
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